The fiber-reinforced composite material is made by combining the reinforcing fiber material and a material which serves as a matrix and is a material which is light-weighted, highly rigid and capable of diversified functional designs. Thus, it is used in a wide variety of fields such as the aerospace field, the transport field, the civil engineering and construction field, the exercise apparatus field and the like. Particularly, fiber reinforced plastics (FRP) made by combining a reinforcing fiber material such as carbon fiber and a glass fiber with a thermosetting resin material constitutes a mainstream. In the fiber-reinforced composite material, a laminated molded body with strength in multiple directions reinforced is used in many cases by laminating prepreg sheets which are reinforced in one direction and setting an aligned direction of each layer in multiple directions.
Since the laminated molded body has a reinforced direction of each layer different from each other, it has a problem that delamination can easily occur. Particularly if the thermosetting resin material such as an epoxy resin is used as a matrix, the thermosetting resin material has a problem that its toughness is low in general and delamination can easily occur. For example, if an impact load or the like is applied to the laminated molded body, even though it appears to have no problem, the delamination occurs inside the molded body, dynamic characteristics as the laminated molded body lower, and the laminated molded body is in a state easy to be broken in many cases.
As a measure against such delamination of the laminated molded body, Patent Literature 1, for example, describes a fiber-reinforced composite material formed of a reinforced fiber formed of a long fiber, a thermosetting resin composition, a particle not soluble in the thermosetting resin composition, and a particle having a resin soluble in the thermosetting resin composition as a material and both particles are localized on a surface, and describes a point that a handling performance of prepreg is maintained by the both particles localized on the surface while an anti-impact characteristic and an inter-layer toughness are improved. Moreover, the prepreg having a reinforced fiber, a matrix resin, and a resin particle as constituent elements is described also in Patent Literature 2.
On the other hand, it has been made clear that a molded body in which thin prepreg sheets in which a thermosetting resin material is impregnated into a reinforced fiber bundle are laminated has dynamic characteristics different from those of the molded body made by laminating prepreg sheets each having a prior-art thickness.
For example, in a molded body in which thin prepreg sheets are laminated, occurrence of delamination is suppressed in tension characteristics as compared with a molded body in which thick prepreg sheets are laminated (Non Patent Literature 1). Moreover, regarding bending characteristics and compression characteristics of the molded body in which thin prepreg sheets are laminated, differences in maximum strength and initial modulus of elasticity of a specimen cut out in various directions are reduced, and it is shown that quasi-isotropic properties are improved as compared with use of thick prepreg sheets (Non Patent Literatures 2 and 3). Moreover, it has become known that the molded body in which thin prepreg sheets are laminated have improved fatigue life as compared with the use of thick prepreg sheets (Non Patent Literature 4).
Regarding impact characteristics, as the result of internal observation after a falling-weight impact load from an off-plate direction to a molded body in which thick prepreg sheets are laminated and a molded body in which thin prepreg sheets are laminated, it was observed that large delamination occurs in an internal layer even in the molded body in which thin prepreg sheets are laminated (Non Patent Literature 5). Regarding compression strength after the impact, slight improvement in strength is found in the molded body in which thin prepreg sheets are laminated as compared with the use of thick prepreg sheets (Non Patent Literature 5), however, as described in Patent Literature 1 and the like, it falls short of improvement of the impact characteristics of the molded body including a layer in which particles are present between layers.